In general, in industrialized countries, garbage and waste, especially household waste, are kept in plastic bags. These plastic bags generally comprise two faces made of plastic joined to one another around their periphery forming an open region. These bags are usually rectangular, although other shapes are possible: for example, the bottom of the bag may be rounded. In the rest of the description, for convenience, reference will be made to rectangular bags, although it is of course understood that the bags according to the present invention are not limited to this shape.
The bags may be prepared from two rectangular plastic sheets, by welding three sides of the rectangle and leaving the fourth side open. They may also be prepared from a single plastic sheet which is folded, either to form the bottom of the bag or to form a lateral side of the bag, two of the other sides being heat welded. In a known manner, the faces of the bag may be joined to one another via a gusset at the bottom and/or along one lateral side, preferably along both lateral sides.
It is also known to produce drawstring bags in which the opening of the bag, however it is made, is bordered by a hem in which a drawstring can slide. The drawstring may consist of a single tape, the two ends of the drawstring being joined together. It may also consist of two tapes, each tape being fixed by each of its ends to the hem. The drawstring is preferably a strip of plastic which can be heat welded.
The hem is generally prepared by folding the plastic sheet parallel to the opening and heat welding it parallel to the edge of the film. The hem may be continuous or formed of two-separate parts. This is in particular the case when the bags are made by heat welding the lateral sides and the hem is formed by folding the plastic sheet before heat welding the lateral sides.
Such bags with plastic, substantially non-elastic drawstrings are described in the applicant's patents EP-953 511 and EP-1 232 954.
A drawstring bag in which the drawstring is elastic or expandable has also been proposed in the prior art, for example in patent U.S. Pat. No. 5,133,607, in German utility model DE-201 10 350-U1 and in international application WO 03/035500. This closed-loop elastic drawstring is characterized in that the length of its periphery is shorter than that of the opening of the bag, in such a way that the user must elastically stretch the drawstring to fix it around the periphery of a receptacle, for example a garbage can. Thus, this drawstring makes it possible to hold the bag elastically on the garbage can, for a wide range of sizes of garbage can, while limiting the risk of the bag slipping inside the garbage can, for example under the weight of the waste inside the bag.
However, the abovementioned elastic drawstring bags have a twofold disadvantage, owing to the presence of relatively deep lateral notches made on the longitudinal edge of opening of the bag. The presence of these relatively wide notches first of all has the disadvantage of not allowing the bag to close completely when the drawstring is tied once the bag has been filled. Thus, when bags full of waste are transported or stored, waste can fall or leak out of these notches. Secondly, the presence of these relatively wide notches reduces the length of the hem in contact with the drawstring, weakening the bag when it is transported full using the elastic drawstring as a handle.
Moreover, all these elastic drawstring bags have the shared disadvantage that the elastic drawstring may not have sufficient tensile strength to support a heavy weight of waste in the bag during transport. Furthermore, even if the tear strength is sufficient, if the weight of waste in the bag is great, there is the risk that the drawstring, which is generally used as a handle by the user when transporting the bag, will stretch elastically, which may cause the bag to drag along the ground or cause it to lower enough that it knocks against obstacles, which is a considerable hindrance for the user.
Also known, from document EP-A-1 013 567, is a plastic drawstring bag comprising an elastic strip whose ends are fixed with a hot melt adhesive to one of the outer faces of the bag, near to but at a distance from the hem enclosing the plastic drawstring. This elastic strip can be grasped from the outside by the user, after the edge of the bag has been folded over the neck of a garbage can, and the user can stretch it elastically so that the strip forms a closed loop which can surround the periphery of the container, holding the bag elastically on the garbage can. Although the elastic strip, preferably made of rubber, can be chosen so as to have a maximum elongation of 800%, this elastic strip preferably has an elastic elongation of below 500%. In a first example, the elastic strip has a relaxed length of around a quarter of the length of the periphery of the container. In a first variant, the elastic strip is stretched so as to extend around only three sides of the container, corresponding to an elastic elongation of around 200%, i.e. a tripling of its length. In another variant, the elastic strip is stretched so as to form a closed loop which completely surrounds the periphery of the container, corresponding to an elastic elongation of around 400%, i.e. five times its relaxed length. In another example, the elastic strip has a length slightly shorter than half the periphery of the container, in such a way that it is necessary to form a closed loop with the elastic strip to hold the bag elastically on the container, corresponding to an elastic elongation of at least 200%, i.e. at least a tripling of its length. Advantageously, this elastic strip is only used to hold the bag elastically on the container, whereas the plastic drawstring is used for tying, so as to close the bag.
Similarly, document EP-A-1 266 837 describes a plastic drawstring bag also comprising an elastic strip which is fixed at its ends to the lateral edges of the bag and is, in a variant, housed in the same hem as the plastic drawstring, or placed on the outer face of said hem. As in document EP-A-1 013 567, to hold the bag elastically on a garbage can, it is necessary to form a closed loop with the elastic strip and to this end it is provided that the elastic elongation of the strip must be greater than 200%, for example 250%, preferably 300% or more.
However, these two documents EP-A-1 013 567 and EP-A-1 266 837, which concern the same type of plastic drawstring bag having an elastic strip for holding the bag on a container, use elastic strips having a high degree of elastic elongation, above 200%, which thus requires the use of special elastic materials, which may be difficult to weld or join to the bag and which are, moreover, difficult to implement in a method for the continuous production of a series of bags, since there is a risk that the high degree of elasticity of the strip will interfere with the many welding, folding and cutting operations necessary to produce, for example, a continuous roll of a series of bags. Specifically, in such a continuous production method, the plastic sheets constituting the faces of the bag and the various drawstrings and strips are held on multiple drive wheels or rolls to ensure minimum tensioning of all these elements. However, a highly elastic strip thus tensioned may deform elastically during the process of production of the series of bags, adversely affecting the quality of the heat welds, or even causing the bag to pucker if these heat welds are not applied correctly.
It is for this reason, moreover, that in document EP-A-1 013 567 the elastic strips are bonded individually and separately to each bag of the series of bags, either transversely to the direction of advance of the series of bags, or parallel to said direction.
The aim of the invention is therefore to propose a bag having an elastic band for fixing the periphery of the bag elastically to a receptacle and which makes it possible to avoid the abovementioned disadvantages. Another aim of the invention is to prevent the risk of waste falling out of the bag after it has been closed. The invention also aims to limit the risk of the elastic band breaking or tearing or the risk of the elastic band deforming during transport of the bag, especially when full of waste.